Non-classical Monocytes Enhance the Efficacy of Immune Checkpoint Inhibitors on Colon Cancer in a Syngeneic Mouse Model

BACKGROUND/AIM

The response rate to immune checkpoint inhibitors (ICIs) is approximately 10%-30% and only in a few cancer types. In the present study, we determined whether non-classical monocytes (NCMs) could enhance ICI efficacy in colon cancer using a syngeneic mouse model.

MATERIALS AND METHODS

The MC38 C57BL/6 mouse colon cancer model was used. Cells collected from the bone marrow of C57BL/6 mice were cultured, and NCMs were fractionated by cell sorting and administered via the tail veins to the mice implanted with MC38 cells. The anti-mouse PD-L1 antibody was administered three times, and tumor volume and overall survival were observed.

RESULTS

More tumors were eradicated and more complete response occurred, after cotreatment with ICIs and NCMs than after treatment with ICIs alone. Moreover, no efficacy was observed when NCMs were administered alone.

CONCLUSION

NCMs enhance ICI efficacy. The underlying mechanisms and clinical applications will be studied in the future.

KLC1-ROS1 Fusion Exerts Oncogenic Properties of Glioma Cells via Specific Activation of JAK-STAT Pathway

Here, we investigated the detailed molecular oncogenic mechanisms of a novel receptor tyrosine kinase (RTK) fusion, KLC1-ROS1, with an adapter molecule, KLC1, and an RTK, ROS1, discovered in pediatric glioma, and we explored a novel therapeutic target for glioma that possesses oncogenic RTK fusion. When wild-type ROS1 and KLC1-ROS1 fusions were stably expressed in the human glioma cell lines A172 and U343MG, immunoblotting revealed that KLC1-ROS1 fusion specifically activated the JAK2-STAT3 pathway, a major RTK downstream signaling pathway, when compared with wild-type ROS1. Immunoprecipitation of the fractionated cell lysates revealed a more abundant association of the KLC1-ROS1 fusion with JAK2 than that observed for wild-type ROS1 in the cytosolic fraction. A mutagenesis study of the KLC1-ROS1 fusion protein demonstrated the fundamental roles of both the KLC1 and ROS1 domains in the constitutive activation of KLC1-ROS1 fusion. Additionally, in vitro assays demonstrated that KLC1-ROS1 fusion upregulated cell proliferation, invasion, and chemoresistance when compared to wild-type ROS1. Combination treatment with the chemotherapeutic agent temozolomide and an inhibitor of ROS1, JAK2, or a downstream target of STAT3, demonstrated antitumor effects against KLC1-ROS1 fusion-expressing glioma cells. Our results demonstrate that KLC1-ROS1 fusion exerts oncogenic activity through serum-independent constitutive activation, resulting in specific activation of the JAK-STAT pathway. Our data suggested that molecules other than RTKs may serve as novel therapeutic targets for RTK fusion in gliomas.

Novel quantitative immunohistochemical analysis for evaluating PD-L1 expression with phosphor-integrated dots for predicting the efficacy of patients with cancer treated with immune checkpoint inhibitors

Introduction

Programmed cell death ligand 1 (PD-L1) expression in tumor tissues is measured as a predictor of the therapeutic efficacy of immune checkpoint inhibitors (ICIs) in many cancer types. PD-L1 expression is evaluated by immunohistochemical staining using 3,3´-diaminobenzidine (DAB) chronogenesis (IHC-DAB); however, quantitative and reproducibility issues remain. We focused on a highly sensitive quantitative immunohistochemical method using phosphor-integrated dots (PIDs), which are fluorescent nanoparticles, and evaluated PD-L1 expression between the PID method and conventional DAB method.

Methods

In total, 155 patients with metastatic or recurrent cancer treated with ICIs were enrolled from four university hospitals. Tumor tissue specimens collected before treatment were subjected to immunohistochemical staining with both the PID and conventional DAB methods to evaluate PD-L1 protein expression.

Results

PD-L1 expression assessed using the PID and DAB methods was positively correlated. We quantified PD-L1 expression using the PID method and calculated PD-L1 PID scores. The PID score was significantly higher in the responder group than in the non-responder group. Survival analysis demonstrated that PD-L1 expression evaluated using the IHC-DAB method was not associated with progression-free survival (PFS) or overall survival (OS). Yet, PFS and OS were strikingly prolonged in the high PD-L1 PID score group.

Conclusion

Quantification of PD-L1 expression as a PID score was more effective in predicting the treatment efficacy and prognosis of patients with cancer treated with ICIs. The quantitative evaluation of PD-L1 expression using the PID method is a novel strategy for protein detection. It is highly significant that the PID method was able to identify a group of patients with a favorable prognosis who could not be identified by the conventional DAB method.

Monocyte subsets associated with the efficacy of anti‑PD‑1 antibody monotherapy

Immune checkpoint inhibitors (ICIs) are among the most notable advances in cancer immunotherapy; however, reliable biomarkers for the efficacy of ICIs are yet to be reported. Programmed death (PD)-ligand 1 (L1)-expressing CD14+ monocytes are associated with shorter overall survival (OS) time in patients with cancer treated with anti-PD-1 antibodies. The present study focused on the classification of monocytes into three subsets: Classical, intermediate and non-classical. A total of 44 patients with different types of cancer treated with anti-PD-1 monotherapy (pembrolizumab or nivolumab) were enrolled in the present study. The percentage of each monocyte subset was investigated, and the percentage of cells expressing PD-L1 or PD-1 within each of the three subsets was further analyzed. Higher pretreatment classical monocyte percentages were correlated with shorter OS (r=-0.32; P=0.032), whereas higher non-classical monocyte percentages were correlated with a favorable OS (r=0.39; P=0.0083). PD-L1-expressing classical monocytes accounted for a higher percentage of the total monocytes than non-classical monocytes with PD-L1 expression. In patients with non-small cell lung cancer (NSCLC), a higher percentage of PD-L1-expressing classical monocytes was correlated with shorter OS (r=-0.60; P=0.012), which is similar to the observation for the whole patient cohort. Comparatively, higher percentages of non-classical monocytes expressing PD-L1 were significantly associated with better OS, especially in patients with NSCLC (r=0.60; P=0.010). Moreover, a higher percentage of non-classical monocytes contributed to prolonged progression-free survival in patients with NSCLC (r=0.50; P=0.042), with similar results for PD-L1-expressing non-classical monocytes. The results suggested that the percentage of monocyte subsets in patients with cancer before anti-PD-1 monotherapy may predict the treatment efficacy and prognosis. Furthermore, more classical monocytes and fewer non-classical monocytes, especially those expressing PD-L1, are involved in shortening OS time, which may indicate the poor efficiency of anti-PD-1 treatment approaches.

A protein kinase D inhibitor suppresses AKT on T cells and antagonizes cancer immunotherapy by anti-PD-1

Antibodies that block the interaction between PD-1 and PD-1 ligands (anti-PD-1) are in clinical use for the treatment of cancer, yet their efficacy is limited. Pre-approved therapies that enhance the effect of anti-PD-1 in combination are beneficial. Small-molecule inhibitors that attenuate T cell receptor signaling are reported to prevent T cell exhaustion and induce memory T cells with stem cell potential, resulting in a durable effector T cell response in combination with anti-PD-1. In search of such targets, we focused on protein kinase D (PKD), which is suggested to be suppressive in both tumor growth and TCR signaling. We report that CRT0066101, a PKD inhibitor (PKDi), suppressed the growth of mouse tumors at a sub-micromolar concentration in vitro. Despite its inhibitory effects on tumors, a single treatment of tumor-bearing mice with PKDi did not inhibit, but rather accelerated tumor growth, and reversed the therapeutic effect of anti-PD-1. Mice treated with PKDi showed reduced T cell infiltration and defects in the generation of effector T cells, compared to those treated with anti-PD-1, suggesting that PKDi inhibited ongoing antitumor responses. Mechanistically, PKDi inhibited phosphorylation of AKT, a primary checkpoint that is reactivated by anti-PD-1. In conclusion, PKD is fundamentally required for T cell reactivation by anti-PD-1; therefore, inhibition of PKD is not appropriate for combination therapy with anti-PD-1. On the other hand, a single dose of PKDi was shown to strongly suppress experimental autoimmunity in mice, indicating that PKDi could be useful for the treatment of immune-related adverse events that are frequently reported in anti-PD-1 therapy.

Current-Voltage Characteristics and Solvent Dissociation of Bipolar Membranes in Organic Solvents

In this work, the chronopotentiometric responses, pH changes, and current-voltage (I-V) characteristics of bipolar membrane (BPM)/LiCl-organic solvent systems were measured and compared with those of the BPM/LiCl-water system. Monohydric alcohols, polyhydric alcohols, and amides were used as organic solvents. The chronopotentiograms and pH changes supported that the organic solvents can dissociate into cations and anions at the BPM interface. It is found that amides cannot dissociate easily at the BPM compared with alcohols. The I-V characteristics showed that both the viscosity and acid-base property of organic solvents substantially influences the dissociation behaviors in addition to the autoprotolysis constant and relative permittivity of the solvents.

Regulatory roles of fibronectin and integrin α5 in reorganization of the actin cytoskeleton and completion of adipogenesis

Cellular differentiation is characterized by changes in cell morphology that are largely determined by actin dynamics. We previously showed that depolymerization of the actin cytoskeleton triggers the differentiation of preadipocytes into mature adipocytes as a result of inhibition of the transcriptional coactivator activity of megakaryoblastic leukemia 1 (MKL1). The extracellular matrix (ECM) influences cell morphology via interaction with integrins, and reorganization of the ECM is associated with cell differentiation. Here we show that interaction between actin dynamics and ECM rearrangement plays a key role in adipocyte differentiation. We found that depolymerization of the actin cytoskeleton precedes disruption and degradation of fibrillar fibronectin (FN) structures at the cell surface after the induction of adipogenesis in cultured preadipocytes. A FN matrix suppressed both reorganization of the actin cytoskeleton into the pattern characteristic of adipocytes and terminal adipocyte differentiation, and these inhibitory effects were overcome by knockdown of integrin α5 (ITGα5). Peroxisome proliferator–activated receptor γ was required for down-regulation of FN during adipocyte differentiation, and MKL1 was necessary for the expression of ITGα5. Our findings suggest that cell-autonomous down-regulation of FN-ITGα5 interaction contributes to reorganization of the actin cytoskeleton and completion of adipocyte differentiation.

Isolation and characterization of neural stem/progenitor cells in the subventricular zone of the naked mole-rat brain

Background

The naked mole-rat (NMR) is the longest-lived rodent with a maximum lifespan of more than 37 years and shows a negligible senescence phenotype, suggesting that tissue stem cells of NMRs are highly capable of maintaining homeostasis. However, the properties of NMR tissue stem cells, including neural stem cells (NSCs), are largely unclear.

Methods

Neural stem/progenitor cells (NS/PCs) were isolated from the subventricular zone of the neonate NMR brain (NMR-NS/PCs) and cultured in neurosphere and adherent culture conditions. Expression of NSC markers and markers of neurons, astrocytes, and oligodendrocytes was analyzed by immunocytochemistry. In adherent culture conditions, the proliferation rate and cell cycle of NMR-NS/PCs were assessed and compared with those of NS/PCs from mice (mouse-NS/PCs). The DNA damage response to γ-irradiation was analyzed by immunocytochemistry and reverse transcription-quantitative PCR.

Results

NMR-NS/PCs expressed several NSC markers and differentiated into neurons, astrocytes, and oligodendrocytes. NMR-NS/PCs proliferated markedly slower than mouse-NS/PCs, and a higher percentage of NMR-NS/PCs than mouse-NS/PCs was in G0/G1 phase. Notably, upon γ-irradiation, NMR-NS/PCs exhibited a faster initiation of the DNA damage response and were less prone to dying than mouse-NS/PCs.

Conclusions

NMR-NS/PCs were successfully isolated and cultured. The slow proliferation of NMR-NS/PCs and their resistance to DNA damage may help to prevent stem cell exhaustion in the brain during the long lifespan of NMRs. Our findings provide novel insights into the mechanism underlying delayed aging of NMRs. Further analysis of NMR tissue stem cells may lead to the development of new strategies that can prevent aging in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-021-00182-7.

Examination of the acute efficacy and safety about aggressive use of tolvaptan for early rising after admission in super-elder patients with congestive heart failure

Background

From August 2015, for shortening of hospitalization period through efficient medical care in acute phase, we had introduced a unique clinical pathway (PATH) for congestive heart failure (CHF) cases. In PATH, since immediate taking of Tolvaptan, which is an strong oral diuretic and approver for use in the treatment of CHF cases since 2010 in Japan, after admission is specified, early diuresis makes it possible to achieve early rising from bed and streamline each medical care such as oxygen inhalation, continuous infusion, and urethral catheterization. Early rising from bed is particularly important for super-elder CHF patients who merge often frail. On the other hand, for super-elder CHF patients, it is feared that aggressive use of Tolvaptan may frequently cause dehydration, renal damage caused by it, or hypernatremia, which is a peculiar side effect about the drug.

Purpose

In this study, we examined the usefulness and safety of active use of Tolvaptan by introducing PATH in patients with super-elder CHF patients.

Methods

We set up three groups, NE group consist of 37 CHF cases (90 years old or over) who admitted in our hospital before (without) introduction of PATH between April 2014 and July 2015, PE group consist of 130 CHF cases (90 years old or over) and PY group consist of 466 CHF cases (under 90 years old) who ware admitted with introduction of PATH between August 2015 and July 2020. And in each group, we investigated various medical conditions in their acute phase after admission and the incidence of adverse events related to oral administration of tolvaptan, and examined the differences between three groups.

Results

Between NE group and PE group, there were no significant differences in mean age, pre-hospital living status, or clinical status at admission (Figure 1). But due to lean and efficient CHF care, the average length of hospitalization period was significantly shorter in PE group. And, in PE group, each medical care was performed as efficiently as in PY group, but the progression of renal damage or hypernatremia that required unscheduled discontinuation of tolvaptan use occurred more frequently in PE group (Figure 2).

Conclusions

Aggressive Tolvaptan use through our unique clinical pathway for congestive heart failure cases seemed to be useful even in super-elder patients. Although we thought that the safety of active use of tolvaptan for super-elder patients was well tolerated considering the results of this study, the incidence of adverse events such as hypernatremia was clearly higher in super-elder patients than in non-super-elder patients. It seemed that we should pay close attention to the clinical data of super-elder patients after introduction of tolvaptan.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Examination about more realistic prognosis evaluation method, how long the patients with congestive heart failure can spend at home

Background

From August 2015, for efficient medical care in congestive heart failure (CHF) cases, we had introduced a unique clinical pathway (PATH) provided the immediate use of Tolvaptan and comprehensive education by multi-disciplinary staff after admission. And by introduction of PATH, we confirmed the shortening effect of hospitalization period with CHF and the suppressive effect of readmission with CHF after discharge. But since almost CHF patients repeat hospitalization and discharge due to change of their medical condition, the investigation for only first readmission rate after discharge is not enough to assess the entire long clinical course of CHF. Recently we found one report about evaluation method for CHF clinical prognosis, how long CHF patients can stay healthy at their own home after discharge within a certain period. This evaluation method is considered to take into account the long clinical course of CHF.

Purpose

We investigated whether the CHF patients introduced PATH on admission could stay longer at their home than CHF patients without PATH.

Methods

Between April 2014 and July 2019, 471 CHF cases, who ware admitted in our hospital at first and could be followed up for at least 1 month after discharge, ware enrolled. We divided them to two groups, PATH- group before introducing PATH (until July 2015, 142 cases), and PATH+ group applied PATH (after August 2015, 329 cases). Between both groups, we investigated the readmission rate (RR) with CHF and the total period (TP) that patients could spend at home within1, 3, 6 and 12month after discharge.

Results

There were no significant differences in mean age, pre-hospital living status, or clinical status at admission between the two groups. On the other hand, due to efficient CHF care, the average length of hospital stay was significantly shorter (figure1). RR within 1, 3, 6 and 12 months after discharge ware all lower in PATH+ group. And TP within 1, 3, 6 and 12 months after discharge ware all longer in PATH+ group (figure2).

Conclusion

By introducing our unique clinical pathway for congestive heart failure cases requiring hospitalization, we could confirm not only the improvement of their conventional clinical prognosis index but also the improvement of their new and more realistic clinical prognosis index after discharge.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Our unique clinical pathway for congestive heart failure cases required admission achieved a dramatic reduction of their hospitalization period and a significant reduction of readmission with heart fa

Background

In recent years, the number of elderly congestive heart failure (CHF) cases has been increasing in Japan with the aging of the population. This tendency is particularly remarkable in rural areas where our facilities are located. After admission with CHF, the hospitalization period (PE) was prolonged due to various complications unique to the elderly, and re-exacerbation of CHF occurred shortly after discharge. Approximately 30% of them were readmitted within one year. From August 2015, for shortening of PE and reduction of CHF readmission through the efficiency of CHF treatment and comprehensive patient education, we had introduced a unique clinical pathway (PATH) that provided the immediate use of Tolvaptan and comprehensive education by multi-disciplinary staff after admission.

Purpose

In this study, we verified whether the improvement of clinical prognosis were achieved by introduction of PATH.

Methods

Between April 2014 and July 2019, 635 CHF cases (764 admissions) ware enrolled. We divided them to two groups, N-group before introducing PATH (198 cases, 262 admissions) and P-group applied PATH (437 cases, 502 admission). Between both groups, we compared the various acute care situation, PE and readmission rate with CHF within 1 year after discharge.

Results

There were no differences between P and N-group in mean age, distribution of underlying illness or daily activity level before admission. There ware not also differences about left ventricle function by echocardiography and various blood test data at admission. The enforcement rate of continuous infusion and the rate of urinary catheter placement were significantly lower in the P-group (71 vs 88%; p<0.0001, 52 vs 63%; p<0.01, respectively). And their enforcement duration was significantly shorter in P-group (4.6±5.3 vs 10.5±9.6 days; p<0.0001, 6.3±7.9 vs 12.8±13.1 days; p<0.0001 respectively). The enforcement rate of cardiac rehabilitation was significantly higher in group P (94 vs 84%; p<0.0001), and the starting time of rehabilitation was significantly earlier (2.9±1.5 vs 6.3±4.8th illness day; p<0.0001). As a result, the average HP was significantly shorter in group P (16.5±13.4 vs 28.6±24.1 days, p<0.0001). The readmission rate with CHF within one year after discharge was significantly lower in group P (23 vs 36%; p<0.001).

Conclusion

By the introduction of our original clinical pathway for congestive heart failure, the efficiency of medical care was achieved and the mean hospitalization period was widely shortened. In addition, by the through comprehensive patient education by multi-disciplinary staff involved in the pathway, the self-restraint life style after discharge seemed to be maintained and the readmission with worsening of heart failure was significantly suppressed.

Funding Acknowledgement

Type of funding source: None

The insulin-PI3K-Rac1 axis contributes to terminal adipocyte differentiation through regulation of actin cytoskeleton dynamics

Adipocyte differentiation is accompanied by a pronounced change in the actin cytoskeleton characterized by the reorganization of filamentous (F)-actin stress fibers into cortical F-actin structures. We previously showed that depolymerization of F-actin stress fibers induced by inactivation of RhoA-ROCK (Rho-associated kinase) signaling acts as a trigger for adipocyte differentiation. The relevance and underlying mechanism of the formation of cortical F-actin structures from depolymerized actin during adipocyte differentiation have remained unclear, however. We have now examined the mechanistic relation between actin dynamics and adipogenic induction. Transient exposure to the actin-depolymerizing agent latrunculin A (LatA) supported the formation of adipocyte-associated cortical actin structures and the completion of terminal adipocyte differentiation in the presence of insulin, whereas long-term exposure to LatA prevented such actin reorganization as well as terminal adipogenesis. Moreover, these effects of insulin were prevented by inhibition of phosphatidylinositol 3-kinase (PI3K)-Rac1 signaling and the actin-related protein 2/3 (Arp2/3) complex which is a critical component of the cortical actin networks. Our findings thus suggest that the insulin-PI3K-Rac1 axis leads to the formation of adipocyte-associated cortical actin structures which is essential for the completion of adipocyte differentiation.

P97 Effect of rhythm control therapy for asymptomatic atrial fibrillation

Background/Introduction

Cather ablation (CA) for atrial fibrillation (AF) as rhythm control therapy has widely spread. However, the indication of CA for the patients with asymptomatic AF is controversial (2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS). 

Purpose

This study was aimed to examine the effect of CA for asymptomatic AF patients.

Methods

In a total of 522 consecutive patients who were hospitalized for the initial CA for AF, 123 patients (23.6%) who were asymptomatic were retrospectively analyzed. "Asymptomatic AF" was defined when the patients had no complaints during the medical interviews. Quality of life (QOL) was evaluated with the AF QOL Questionnaire score (AFQLQ, invented by the Japanese Society of Electrocardiology) before CA and at 1 year after a single CA.

Results

A total of 79 patients were persistent AF (64.2%). Sinus rhythm maintenance rate at 3 yeas after CA was 57.0% in a single session and 84.8% in multiple sessions. In cardiac echo data at baseline, 3 months, 6 months, and 1 year after CA, left ventricular ejection fraction (LVEF) and left atrium diameter (LAD) were improved in the initial three months after a single CA (LVEF; 62.8 ± 8.0%→64.4 ± 6.5%, p = 0.045, LAD; 39.7 ± 6.1mm→35.3 ± 7.0mm, p = 0.0002). In LA volume measured with CT before and after CA, LA reverse remodeling was observed (102.7 ± 32.3ml→72.4 ± 24.1ml, p<.0001). In AFQLQ2 (severity of symptoms), there was no significant difference (16.3 ± 2.2→15.9 ± 1.7 out of 18, p = 0.69). However, in AFQLQ1 (frequency of symptoms) and AFQLQ3 (limitations of activities and mental anxiety), the score was improved (20.2 ± 4.5→23.4 ± 1.1 out of 24, p<.0001 and 47.6 ± 7.8→51.3 ± 6.1 out of 56, p = 0.0001).  Moreover, in low LVEF patients (LVEF < 50%, n = 8), LVEF was remarkably improved (44.1 ± 4.0%→56.3 ± 10.8%, p = 0.034).

Conclusions

The improvement of LVEF and LA reverse remodeling can be expected at the early stage after CA, because of the reduction of AF burden. Moreover, the further improvement of QOL can be expected after CA, even in the patients with "asymptomatic" AF.

IMP dehydrogenase-2 drives aberrant nucleolar activity and promotes tumorigenesis in glioblastoma

In many cancers, high proliferation rates correlate with elevation of rRNA and tRNA levels, and nucleolar hypertrophy. However, the underlying mechanisms linking increased nucleolar transcription and tumorigenesis are only minimally understood. Here we show that IMP dehydrogenase-2 (IMPDH2), the rate-limiting enzyme for de novo guanine nucleotide biosynthesis, is overexpressed in the highly lethal brain cancer glioblastoma. This leads to increased rRNA and tRNA synthesis, stabilization of the nucleolar GTP-binding protein nucleostemin, and enlarged, malformed nucleoli. Pharmacological or genetic inactivation of IMPDH2 in glioblastoma reverses these effects and inhibits cell proliferation, whereas untransformed glia cells are unaffected by similar IMPDH2 perturbations. Impairment of IMPDH2 activity triggers nucleolar stress and growth arrest of glioblastoma cells even in the absence of functional p53. Our results reveal that upregulation of IMPDH2 is a prerequisite for the occurance of aberrant nucleolar function and increased anabolic processes in glioblastoma, which constitutes a primary event in gliomagenesis.

ROCK Inhibition Induces Terminal Adipocyte Differentiation and Suppresses Tumorigenesis in Chemoresistant Osteosarcoma Cells

Tumors comprise heterogeneous cell types including cancer stem cells (CSC), progenitor cells, and differentiated cells. Chemoresistance is a potential cause of relapse and a key characteristic of CSC, but the development of novel therapeutic approaches for targeting these cells has been limited. We previously established osteosarcoma-initiating (OSi) cells by introducing the gene for c-Myc into bone marrow stromal cells of Ink4a/Arf knockout mice. These OSi cells are composed of two distinct clones: highly tumorigenic cells (AX cells), similar to bipotent committed osteochondral progenitor cells, and tripotent cells of low tumorigenicity (AO cells), similar to mesenchymal stem cells. Here we show that depolymerization of the actin cytoskeleton induces terminal adipocyte differentiation and suppresses tumorigenesis in chemoresistant OSi cells. In contrast to AX cells, AO cells were highly resistant to conventional chemotherapeutic agents such as doxorubicin and were thus identified as chemoresistant cells. Inhibition of Rho-associated coiled-coil containing protein kinase (ROCK) elicited terminal adipocyte differentiation in chemoresistant AO cells through negative regulation of the transcriptional coactivator megakaryoblastic leukemia 1 associated with actin depolymerization. The clinically administered ROCK inhibitor fasudil significantly suppressed growth in vitro and tumorigenicity in vivo of chemoresistant AO cells as well as of OSi cells. Our findings thus suggest a new therapeutic strategy based on the induction of trans-terminal differentiation via modulation of actin cytoskeleton dynamics for therapy-resistant osteosarcoma stem cells. SIGNIFICANCE: These findings suggest that induction of trans-terminal differentiation through regulation of actin dynamics is a potential novel therapeutic approach for targeting chemoresistant stem-like tumor cells.

Abstract LB-334: xCT promotes malignant phenotypes in EGFR-expressing glioma

Malignant glioma such as glioblastoma is a cancer still difficult to treat. System xc(-) is composed of xCT and CD98hc subunits and functions as a plasma membrane antiporter for the uptake of extracellular cystine in exchange for intracellular glutamate, which has been reported to be involved in malignant phenotypes of glioma cells. However, the underlying mechanism of xCT regulation in glioma is not elucidated. Here we show that the epidermal growth factor receptor (EGFR) interacts with xCT and thereby promotes its cell surface expression and function in human glioma cells. EGFR-expressing glioma cells manifested both enhanced antioxidant capacity as a result of increased cystine uptake as well as increased extracellular glutamate which promotes glioma matrix invasion. Imaging mass spectrometry also revealed that brain tumors formed in mice by human glioma cells stably overexpressing EGFR contained higher levels of reduced glutathione compared with those formed by parental cells. Targeted inhibition of xCT suppressed the EGFR-dependent enhancement of antioxidant capacity in glioma cells as well as tumor growth and invasiveness. Our findings propose that xCT is a promising therapeutic target in EGFR-overexpressing malignant glioma.

Citation Format: Kenji Tsuchihashi, Shogo Okazaki, Momoko Yoshikawa, Ryo Seishima, Oltea Sampetrean, Nobuyuki Onishi, Hiroaki Wakimoto, Frank Furnari, Eishi Baba, Koichi Akashi, Hideyuki Saya, Osamu Nagano. xCT promotes malignant phenotypes in EGFR-expressing glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-334. doi:10.1158/1538-7445.AM2017-LB-334

Activation of Transforming Growth Factor Beta 1 Signaling in Gastric Cancer-associated Fibroblasts Increases Their Motility, via Expression of Rhomboid 5 Homolog 2, and Ability to Induce Invasiveness of Gastric Cancer Cells

BACKGROUND & AIMS

Fibroblasts that interact with cancer cells are called cancer-associated fibroblasts (CAFs), which promote progression of different tumor types. We investigated the characteristics and functions of CAFs in diffuse-type gastric cancers (DGCs) by analyzing features of their genome and gene expression patterns.

METHODS

We isolated CAFs and adjacent non-cancer fibroblasts (NFs) from 110 gastric cancer (GC) tissues from patients who underwent gastrectomy in Japan from 2008 through 2016. Cells were identified using specific markers of various cell types by immunoblot and flow cytometry. We selected pairs of CAFs and NFs for whole-exome and RNA sequencing analyses, and compared expression of specific genes using quantitative reverse transcription PCR. Protein levels and phosphorylation were compared by immunoblot and immunofluorescence analyses. Rhomboid 5 homolog 2 (RHBDF2) was overexpressed from a transgene in fibroblasts or knocked down using small interfering RNAs. Motility and invasiveness of isolated fibroblasts and GC cell lines (AGS, KATOIII, MKN45, NUGC3, NUGC4, OCUM-2MD3 and OCUM-12 cell lines) were quantified by real-time imaging analyses. We analyzed 7 independent sets of DNA microarray data from patients with GC and associated expression levels of specific genes with patient survival times. Nude mice were given injections of OCUM-2MD3 in the stomach wall; tumors and metastases were collected and analyzed by immunohistochemistry.

RESULTS

Many of the genes with increased expression in CAFs compared with NFs were associated with transforming growth factor beta 1 (TGFB1) activity. When CAFs were cultured in extracellular matrix, they became more motile than NFs; DGC cells incubated with CAFs were also more motile and invasive in vitro than DGC cells not incubated with CAFs. When injected into nude mice, CAF-incubated DGC cells invaded a greater number of lymphatic vessels than NF-incubated DGC cells. We identified RHBDF2 as a gene overexpressed in CAFs compared with NFs. Knockdown of RHBDF2 in CAFs reduced their elongation and motility in response to TGFB1, whereas overexpression of RHBDF2 in NFs increased their motility in extracellular matrix. RHBDF2 appeared to regulate oncogenic and non-canonical TGFB1 signaling. Knockdown of RHBDF2 in CAFs reduced cleavage of the TGFB receptor 1 (TGFBR1) by ADAM metallopeptidase domain 17 (ADAM17 or TACE) and reduced expression of genes that regulate motility. Incubation of NFs with in interleukin 1 alpha (IL1A), IL1B or tumor necrosis factor, secreted by DGCs, increased fibroblast expression of RHBDF2. Simultaneous high expression of these cytokines in GC samples was associated with shorter survival times of patients.

CONCLUSIONS

In CAFs isolated from human DGCs, we observed increased expression of RHBDF2, which regulates TGFB1 signaling. Expression of RHBDF2 in fibroblasts is induced by inflammatory cytokines (such as IL1A, IL1B, and tumor necrosis factor) secreted by DGCs. RHBDF2 promotes cleavage of TGFBR1 by activating TACE and motility of CAFs in response to TGFB1. These highly motile CAFs induce DGCs to invade extracellular matrix and lymphatic vessels in nude mice.

Simvastatin-Induced Apoptosis in Osteosarcoma Cells: A Key Role of RhoA-AMPK/p38 MAPK Signaling in Antitumor Activity

Osteosarcoma is the most common type of primary bone tumor, novel therapeutic agents for which are urgently needed. To identify such agents, we screened a panel of approved drugs with a mouse model of osteosarcoma. The screen identified simvastatin, which inhibited the proliferation and migration of osteosarcoma cells in vitro Simvastatin also induced apoptosis in osteosarcoma cells in a manner dependent on inhibition of the mevalonate biosynthetic pathway. It also disrupted the function of the small GTPase RhoA and induced activation of AMP-activated protein kinase (AMPK) and p38 MAPK, with AMPK functioning upstream of p38 MAPK. Inhibitors of AMPK or p38 MAPK attenuated the induction of apoptosis by simvastatin, whereas metformin enhanced this effect of simvastatin by further activation of AMPK. Although treatment with simvastatin alone did not inhibit osteosarcoma tumor growth in vivo, its combination with a fat-free diet induced a significant antitumor effect that was enhanced further by metformin administration. Our findings suggest that simvastatin induces apoptosis in osteosarcoma cells via activation of AMPK and p38 MAPK, and that, in combination with other approaches, it holds therapeutic potential for osteosarcoma. Mol Cancer Ther; 16(1); 182-92. ©2016 AACR.

The EGF Receptor Promotes the Malignant Potential of Glioma by Regulating Amino Acid Transport System xc(-)

Extracellular free amino acids contribute to the interaction between a tumor and its microenvironment through effects on cellular metabolism and malignant behavior. System xc(-) is composed of xCT and CD98hc subunits and functions as a plasma membrane antiporter for the uptake of extracellular cystine in exchange for intracellular glutamate. Here, we show that the EGFR interacts with xCT and thereby promotes its cell surface expression and function in human glioma cells. EGFR-expressing glioma cells manifested both enhanced antioxidant capacity as a result of increased cystine uptake, as well as increased glutamate, which promotes matrix invasion. Imaging mass spectrometry also revealed that brain tumors formed in mice by human glioma cells stably overexpressing EGFR contained higher levels of reduced glutathione compared with those formed by parental cells. Targeted inhibition of xCT suppressed the EGFR-dependent enhancement of antioxidant capacity in glioma cells, as well as tumor growth and invasiveness. Our findings establish a new functional role for EGFR in promoting the malignant potential of glioma cells through interaction with xCT at the cell surface. Cancer Res; 76(10); 2954-63. ©2016 AACR.

Arsenic trioxide sensitizes glioblastoma to a myc inhibitor

Glioblastoma multiforme (GBM) is associated with high mortality due to infiltrative growth and recurrence. Median survival of the patients is less than 15 months, increasing requirements for new therapies. We found that both arsenic trioxide and 10058F4, an inhibitor of Myc, induced differentiation of cancer stem-like cells (CSC) of GBM and that arsenic trioxide drastically enhanced the anti-proliferative effect of 10058F4 but not apoptotic effects. EGFR-driven genetically engineered GBM mouse model showed that this cooperative effect is higher in EGFRvIII-expressing INK4a/Arf^-/- neural stem cells (NSCs) than in control wild type NSCs. In addition, treatment of GBM CSC xenografts with arsenic trioxide and 10058F4 resulted in significant decrease in tumor growth and increased differentiation with concomitant decrease of proneural and mesenchymal GBM CSCs in vivo. Our study was the first to evaluate arsenic trioxide and 10058F4 interaction in GBM CSC differentiation and to assess new opportunities for arsenic trioxide and 10058F4 combination as a promising approach for future differentiation therapy of GBM.

Synergistic antiproliferative effect of imatinib and adriamycin in platelet-derived growth factor receptor-expressing osteosarcoma cells

Osteosarcoma (OS) is the most frequent primary solid malignant tumor of bone. Its prognosis remains poor in the substantial proportion of patients who do not respond to chemotherapy and novel therapeutic options are therefore needed. We previously established a mouse model that mimics the aggressive behavior of human OS. Enzyme-linked immunosorbent assay-based screening of such mouse tumor lysates identified platelet-derived growth factor–BB (PDGF-BB) as an abundant soluble factor, the gene for which was expressed dominantly in surrounding non-malignant cells of the tumor, whereas that for the cognate receptor (PDGF receptor β) was highly expressed in OS cells. Platelet-derived growth factor-BB induced activation of both MEK–ERK and phosphatidylinositol 3-kinase–protein kinase B signaling pathways and promoted survival in OS cells deprived of serum, and these effects were blocked by the PDGF receptor inhibitor imatinib. However, these actions of PDGF-BB and imatinib were mostly masked in the presence of serum. Whereas imatinib alone did not manifest an antitumor effect in mice harboring OS tumors, combined treatment with imatinib and adriamycin exerted a synergistic antiproliferative effect on OS cells in vivo. These results suggest that treatment of OS with imatinib is effective only when cell survival is dependent on PDGF signaling or when imatinib is combined with another therapeutic intervention that renders the tumor cells susceptible to imatinib action, such as by inducing cellular stress.

Abstract 4342: Crosstalk between initiating cells with different metabolism in a murine model of malignant glioma

Background

The metabolic preference of malignant glioma for glycolysis as an energy source is a potential therapeutic target. As a result of the cellular heterogeneity of these tumors, however, the relation between glycolytic preference, tumor formation, and tumor cell clonogenicity has remained unknown. To address this issue, we analyzed the metabolic profiles of isogenic glioma-initiating cells (GICs) in a mouse model.

Methods

GICs were established by overexpression of H-RasV12 in Ink4a/Arf-null neural stem cells. Subpopulations of these cells were obtained by single-cell cloning, and clones differing in extracellular acidification potential were assessed for metabolic characteristics by quantification of intra- and extracellular metabolites. Tumorigenicity was assessed by implantation of 100 cells of each subpopulation into the forebrain of wild-type mice. Tumors were examined for pathological features of glioma and expression of glycolytic enzymes.

Results

Malignant transformation of neural stem cells resulted in a shift in metabolism characterized by a significant increase in glucose uptake and lactic acid production. Clonal populations of GICs also manifested pronounced differences in their metabolic profiles. Certain GICs consumed more glucose and produced more lactate, while others had higher oxygen consumption. These differences were reflected in the levels of intracellular metabolites and they were paralleled by a differential expression of glycolytic enzymes such as hexokinase 2 and pyruvate kinase M2. GIC clones with different metabolic profiles had the same level of tumorigenic ability and the tumors formed by all types of GICs displayed the histopathological features of glioblastoma. However, the differential expression of the glycolytic enzymes was also evident in the tumors formed by each of the clones. Implantation of a mix of GICs with different metabolic profiles showed that clones with higher glycolytic ability were the major component of the tumor mass and that they provided a scaffold for the less glycolytic clones, supporting their expansion.

Conclusions

The metabolic characteristics of glioma cells appear early during malignant transformation and persist until the late stages of tumor formation. Even isogenic clones may be heterogeneous in terms of metabolic features, however, and this heterogeneity may play a role in tumor cell proliferation and survival. Our results suggest that a more detailed understanding of the metabolic profile of malignant gliomas is imperative for their effective therapeutic targeting.

Citation Format: Oltea Sampetrean, Isako Saga, Shunsuke Shibao, Jun Okubo, Satoru Osuka, Nobuyuki Onishi, Hideyuki Saya. Crosstalk between initiating cells with different metabolism in a murine model of malignant glioma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4342. doi:10.1158/1538-7445.AM2014-4342

Abstract 2041: Development and analysis of mouse brain tumor models derived from neural stem cells expressing activated ALK

Neural Stem Cells (NSCs), having self-renewal and multipotent ability, are considered one of the cells-of-origin of glioblastoma maltifome (GBM). Although NSCs can be enriched in neurosphere floating culture with serum-free media containing EGF/FGF as a classical method, neurosphere is composed of not only NSCs but also differentiated and apoptotic cells. Therefore, we utilize the method for efficient derivation of NSCs with long-term self-renewal and differentiate capacity in adherent culture. Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase first identified in a chromosomal translocation associated with anaplastic large cell lymphomas. Subsequently, new ALK translocations were found in a fraction of non-small-cell lung cancers and in other solid tumors. The function of full-length ALK is involved in neuronal cell differentiation, regeneration and synapse formation. Recently, gene amplification and mutations of full-length ALK were identified in neuroblastoma. Furthermore, it is reported that ALK and PTN, ligand of ALK, are required for maintenance of the stem cell population in GBM. Although constitutive activation of ALK signaling results in cell transformation, little is known about the tumorigenic mechanisms induced by activated ALK. We reasoned that ALK activity has a crucial role in GBM. To verify this hypothesis, human GBM stem cell lines were treated with crizotinib, ALK inhibitor. Crizotinib could suppress the proliferation of human GBM stem cell lines in dose-dependent-manner. Next, we have established a stable mouse model of brain tumor transplanting the genetically modified NSCs. Active mutant of H-RAS could transform the Ink4a/Arf KO NSCs but not WT NSCs. However, transplanting of WT NSCs transduced activated ALK could rapidly formed highly proliferative and invasive brain tumors. Histological characteristics of these tumors resembled human GBM phenotype demonstrating necrosis, perivascular cuffing and giant cell formation. Although the activated H-RAS increased expression of Ink4a in WT NSCs, but the activated ALK never changed. On the basis of these findings, we propose a specific regulation against tumor suppressor genes by activated ALK.

Citation Format: Nobuyuki Onishi, Oltea Sampetrean, Eiji Sugihara, Hideyuki Saya. Development and analysis of mouse brain tumor models derived from neural stem cells expressing activated ALK. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2041. doi:10.1158/1538-7445.AM2014-2041

Regulation of MKL1 via actin cytoskeleton dynamics drives adipocyte differentiation

Cellular differentiation is regulated through activation and repression of defined transcription factors. A hallmark of differentiation is a pronounced change in cell shape, which is determined by dynamics of the actin cytoskeleton. Here we show that regulation of the transcriptional coactivator MKL1 (megakaryoblastic leukemia 1) by actin cytoskeleton dynamics drives adipocyte differentiation mediated by peroxisome proliferator-activated receptor γ (PPARγ), a master transcriptional regulator of adipogenesis. Induction of adipocyte differentiation results in disruption of actin stress fibres through downregulation of RhoA-ROCK signalling. The consequent rapid increase in monomeric G-actin leads to the interaction of G-actin with MKL1, which prevents nuclear translocation of MKL1 and allows expression of PPARγ followed by adipogenic differentiation. Moreover, we found that MKL1 and PPARγ act in a mutually antagonistic manner in the adipocytic differentiation programme. Our findings thus provide new mechanistic insight into the relation between the dynamics of cell shape and transcriptional regulation during cellular differentiation.

IGF1 receptor signaling regulates adaptive radioprotection in glioma stem cells

Cancer stem cells (CSCs) play an important role in disease recurrence after radiation treatment as a result of intrinsic properties such as high DNA repair capability and antioxidative capacity. It is unclear, however, how CSCs further adapt to escape the toxicity of the repeated irradiation regimens used in clinical practice. Here, we have exposed a population of murine glioma stem cells (GSCs) to fractionated radiation in order to investigate the associated adaptive changes, with the ultimate goal of identifying a targetable factor that regulates acquired radioresistance. We have shown that fractionated radiation induces an increase in IGF1 secretion and a gradual upregulation of the IGF type 1 receptor (IGF1R) in GSCs. Interestingly, IGF1R upregulation exerts a dual radioprotective effect. In the resting state, continuous IGF1 stimulation ultimately induces downregulation of Akt/extracellular-signal-regulated kinases (ERK) and FoxO3a activation, which results in slower proliferation and enhanced self-renewal. In contrast, after acute radiation, the abundance of IGF1R and increased secretion of IGF1 promote a rapid shift from a latent state toward activation of Akt survival signaling, protecting GSCs from radiation toxicity. Treatment of tumors formed by the radioresistant GSCs with an IGF1R inhibitor resulted in a marked increase in radiosensitivity, suggesting that blockade of IGF1R signaling is an effective strategy to reverse radioresistance. Together, our results show that GSCs evade the damage of repeated radiation not only through innate properties but also through gradual inducement of resistance pathways and identify the dynamic regulation of GSCs by IGF1R signaling as a novel mechanism of adaptive radioprotection.

Acquired expression of NFATc1 downregulates E-cadherin and promotes cancer cell invasion

NFATc1 is a transcription factor that regulates T-cell development, osteoclastogenesis, and macrophage function. Given that T cells, osteoclasts, and macrophages in the tumor microenvironment are thought to modulate tumor progression, tumor cells may acquire NFATc1 expression through fusion with these NFATc1-expressing normal cells. We here revealed that a small proportion of tumor cells in human carcinoma specimens expressed NFATc1. To investigate the consequences of NFATc1 acquisition by tumor cells, we established A549 and MCF7 cell lines expressing a constitutively active form of NFATc1 (NFATc1CA) in an inducible manner. The expression of NFATc1CA promoted cancer cell invasion in association with changes in cell morphology. Analysis of gene expression and RNA interference experiments revealed that NFATc1CA suppressed E-cadherin expression by upregulating the transcriptional repressors Snail and Zeb1 in a manner independent of TGF-β signaling. Induced expression of NFATc1CA also downregulated E-cadherin expression and increased invasive activity in tumor xenografts in vivo. Our results thus suggest that the acquisition of NFATc1 expression contributes to tumor progression.

Targeting Aurora B to the equatorial cortex by MKlp2 is required for cytokinesis

Although Aurora B is important in cleavage furrow ingression and completion during cytokinesis, the mechanism by which kinase activity is targeted to the cleavage furrow and the molecule(s) responsible for this process have remained elusive. Here, we demonstrate that an essential mitotic kinesin MKlp2 requires myosin-II for its localization to the equatorial cortex, and this event is required to recruit Aurora B to the equatorial cortex in mammalian cells. This recruitment event is also required to promote the highly focused accumulation of active RhoA at the equatorial cortex and stable ingression of the cleavage furrow in bipolar cytokinesis. Specifically, in drug-induced monopolar cytokinesis, targeting Aurora B to the cell cortex by MKlp2 is essential for cell polarization and furrow formation. Once the furrow has formed, MKlp2 further recruits Aurora B to the growing furrow. This process together with continuous Aurora B kinase activity at the growing furrow is essential for stable furrow propagation and completion. In contrast, a MKlp2 mutant defective in binding myosin-II does not recruit Aurora B to the cell cortex and does not promote furrow formation during monopolar cytokinesis. This mutant is also defective in maintaining the ingressing furrow during bipolar cytokinesis. Together, these findings reveal that targeting Aurora B to the cell cortex (or the equatorial cortex) by MKlp2 is essential for the maintenance of the ingressing furrow for successful cytokinesis.

Twist2 functions as a tumor suppressor in murine osteosarcoma cells

The epithelial-mesenchymal transition (EMT) contributes to the malignant progression of cancer cells including acquisition of the ability to undergo metastasis. However, whereas EMT-related transcription factors (EMT-TF) are known to play an important role in the malignant progression of epithelial tumors, their role in mesenchymal tumors remains largely unknown. We show that expression of the gene for Twist2 is downregulated in human osteosarcoma and correlates inversely with tumorigenic potential in mouse osteosarcoma. Forced expression of Twist2 in highly tumorigenic murine osteosarcoma cells induced a slight inhibition of cell growth in vitro but markedly suppressed tumor formation in vivo. Conversely, knockdown of Twist2 in osteosarcoma cells with a low tumorigenic potential promoted tumor formation in vivo, suggesting that Twist2 functions as a tumor suppressor in osteosarcoma cells. Furthermore, Twist2 induced expression of fibulin-5, which has been reported as a tumor suppressor. Medium conditioned by mouse osteosarcoma cells overexpressing Twist2 inhibited expression of the MMP9 gene as well as invasion in mouse embryonic fibroblasts, and forced expression of Twist2 in osteosarcoma cells suppressed MMP9 gene expression in tumor tissue. Data from the present study suggest that Twist2 inhibits formation of a microenvironment conducive to tumor growth and thereby attenuates tumorigenesis in osteosarcoma.

Abstract 238: IGF1 receptor signaling regulates adaptive radioprotection in glioma stem cells

Background: Cancer stem cells play an important role in disease recurrence after radiation treatment as a result of intrinsic properties such as quiescence and high DNA repair capability. It is unclear, however, how cancer stem cells further adapt to escape the toxicity of the repeated irradiation regimens used in clinical practice. Here, we have exposed a population of murine glioma stem cells (GSCs) to fractionated radiation in order to investigate the associated adaptive changes, with the ultimate goal of identifying a targetable factor that regulates acquired radioresistance.

Methods: Initial tumors were formed by implantation of Ink4a/Arf -/- neural stem cells overexpressing H-RASV12 into the forebrain of wild-type mice. GSCs purified from the tumors were then grown as tumorspheres (TS), with a subgroup, TS-RR, surviving repeated radiation (12x 5Gy). The two types of cells, their subclones and allografts were compared to identify differentially expressed factors that underlie acquired radioresistance.

Results: TS-RR were more resistant than TS to further radiation, both in vitro and in vivo. Analysis of the subclones showed that even the most resistant TS subclones did not reach the radioresistance level of TS-RR, suggesting that TS-RR may have acquired radioresistance de novo during the repeated irradiation. Analysis of the molecular changes induced in TS during fractionated radiation revealed an increase in IGF1 secretion and a gradual up-regulation of the IGF type 1 receptor (IGF1R). Interestingly, IGF1R up-regulation exerted a dual radioprotective effect: in the resting state, continuous IGF1 stimulation ultimately induced down-regulation of Akt/ERK and FoxO3a activation, which resulted in slower proliferation and enhanced self-renewal. In contrast, after acute radiation, the abundance of IGF1R and increased secretion of IGF1 promoted a rapid shift from a latent state towards activation of Akt survival signaling, protecting GSCs from radiation toxicity. Treatment of tumors formed by the radioresistant GSCs with an IGF1R inhibitor resulted in a marked increase in radiosensitivity.

Conclusion: Our results show that GSCs can evade the damage of repeated radiation not only through innate properties, but also by establishing an IGF1-IGF1R autocrine trophic loop, which results in acquired resistance to radiation. Elucidation of stem-cell-specific adaptive radioprotection mechanisms and identification of targetable key factors are crucial to the refinement of radiosensitizing strategies and prevention of tumor relapse.

Citation Format: Satoru Osuka, Oltea Sampetrean, Takatsune Shimizu, Isako Saga, Nobuyuki Onishi, Eiji Sugihara, Jun Okubo, Satoshi Fujita, Shingo Takano, Akira Matsumura, Hideyuki Saya. IGF1 receptor signaling regulates adaptive radioprotection in glioma stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 238. doi:10.1158/1538-7445.AM2013-238

xCT inhibition depletes CD44v-expressing tumor cells that are resistant to EGFR-targeted therapy in head and neck squamous cell carcinoma

The targeting of antioxidant systems that allow stem-like cancer cells to avoid the adverse consequences of oxidative stress might be expected to improve the efficacy of cancer treatment. Here, we show that head and neck squamous cell carcinoma (HNSCC) cells that express variant isoforms of CD44 (CD44v) rely on the activity of the cystine transporter subunit xCT for control of their redox status. xCT inhibition selectively induces apoptosis in CD44v-expressing tumor cells without affecting CD44v-negative differentiated cells in the same tumor. In contrast to CD44v-expressing undifferentiated cells, CD44v-negative differentiated cells manifest EGF receptor (EGFR) activation and rely on EGFR activity for their survival. Combined treatment with inhibitors of xCT-dependent cystine transport and of EGFR resulted in a synergistic reduction of EGFR-expressing HNSCC tumor growth. Thus, xCT-targeted therapy may deplete CD44v-expressing undifferentiated HNSCC cells and concurrently sensitize the remaining differentiating cells to available treatments including EGFR-targeted therapy.

Abstract P2-04-01: Development of mouse breast cancer models based on induced cancer stem cells (iCSC)

Breast cancer is one of the leading causes of death in women worldwide. To develop novel therapeutic approaches for the refractory cases, the mouse models which recapitulate the tumor tissues biologically and pathologically similar to human breast cancer are required. Although xenograft models of established cell lines in immune-deficient mice are frequently used for preclinical experiments, such xenograft models are not sufficient because the heterogenous structure based on the microenvironment and the intrinsic characteristics of cancer cells is not correctly formed.

In this study, we have established induced cancer stem cells (iCSC) from normal mouse mammary stem/progenitor cells through minimal required genetic manipulations and generated mouse breast cancer models by inoculating the iCSCs in the mammary fat pads. Initially, we established iCSC by introducing the H-RasV12 into Ink4a/Arf-knockout mammary stem/progenitor cells and this iCSC formed tumor similar to human triple negative breast cancer in mouse. This finding suggested that two genetic events, an activation of oncogenic signal and a tumor suppressor inactivation, are required for generating the breast cancer iCSC.

Anaplastic Lymphoma Kinase (ALK) gene, which encodes a receptor tyrosine kinase, was reported to be amplified and/or overexpressed up to 86% of patients in inflammatory breast cancer, and pleiotrophin (PTN), which is a physiological ligand for ALK, was also shown to be highly expressed in about 60% of human breast cancers. Therefore, we hypothesized that ALK pathway is involved in tumorigenesis of breast cancers and, then, attempted to generate iCSC by using ALK gene. Interestingly, we found that one of the naturally occurring mutations of ALK is sufficient for generating iCSC and tumor formation in vivo without any prior tumor suppressor inactivation. The ALK-induced iCSCs developed highly aggressive breast cancers in mice. Furthermore, the tumor formation was significantly suppressed when the ALK-induced iCSCs were generated by using mammary stem/progenitor cells derived from mouse deficient in CD44 which is a CSC marker. We have recently revealed a role of CD44, in particular that of a variant isoform (CD44v), in the protection of CSCs from high levels of oxidative stress derived from both tumor cells and their microenvironment (Cancer Cell 19: 387–400, 2011; Cancer Res 72: 1438–1448, 2012; Nat Commun 3: 883, 2012). We will discuss the underlying mechanism of ALK-induced tumorigenesis and a role of CD44 in the CSC functions.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-04-01.

Up-regulation of Imp3 confers in vivo tumorigenicity on murine osteosarcoma cells

Osteosarcoma is a high-grade malignant bone tumor that manifests ingravescent clinical behavior. The intrinsic events that confer malignant properties on osteosarcoma cells have remained unclear, however. We previously established two lines of mouse osteosarcoma cells: AX cells, which are able to form tumors in syngeneic mice, and AXT cells, which were derived from such tumors and acquired an increased tumorigenic capacity during tumor development. We have now identified Igf2 mRNA-binding protein3 (Imp3) as a key molecule responsible for this increased tumorigenicity of AXT cells in vivo. Imp3 is consistently up-regulated in tumors formed by AX cells, and its expression in these cells was found to confer malignant properties such as anchorage-independent growth, loss of contact inhibition, and escape from anoikis in vitro. The expression level of Imp3 also appeared directly related to tumorigenic ability in vivo which is the critical determination for tumor-initiating cells. The effect of Imp3 on tumorigenicity of osteosarcoma cells did not appear to be mediated through Igf2-dependent mechanism. Our results implicate Imp3 as a key regulator of stem-like tumorigenic characteristics in osteosarcoma cells and as a potential therapeutic target for this malignancy.

Modulation of glucose metabolism by CD44 contributes to antioxidant status and drug resistance in cancer cells

An increased glycolytic flux accompanied by activation of the pentose phosphate pathway (PPP) is implicated in chemoresistance of cancer cells. In this study, we found that CD44, a cell surface marker for cancer stem cells, interacts with pyruvate kinase M2 (PKM2) and thereby enhances the glycolytic phenotype of cancer cells that are either deficient in p53 or exposed to hypoxia. CD44 ablation by RNA interference increased metabolic flux to mitochondrial respiration and concomitantly inhibited entry into glycolysis and the PPP. Such metabolic changes induced by CD44 ablation resulted in marked depletion of cellular reduced glutathione (GSH) and increased the intracellular level of reactive oxygen species in glycolytic cancer cells. Furthermore, CD44 ablation enhanced the effect of chemotherapeutic drugs in p53-deficient or hypoxic cancer cells. Taken together, our findings suggest that metabolic modulation by CD44 is a potential therapeutic target for glycolytic cancer cells that manifest drug resistance.

Fibroblast growth factor-2 is an important factor that maintains cellular immaturity and contributes to aggressiveness of osteosarcoma

Osteosarcoma is the most frequent, nonhematopoietic, primary malignant tumor of bone. Histopathologically, osteosarcoma is characterized by complex mixtures of different cell types with bone formation. The role of environmental factors in the formation of such a complicated tissue structure as osteosarcoma remains to be elucidated. Here, a newly established murine osteosarcoma model was used to clarify the roles of environmental factors such as fibroblast growth factor-2 (Fgf2) or leukemia-inhibitory factor (Lif) in the maintenance of osteosarcoma cells in an immature state. These factors were highly expressed in tumor environmental stromal cells, rather than in osteosarcoma cells, and they potently suppressed osteogenic differentiation of osteosarcoma cells in vitro and in vivo. Further investigation revealed that the hyperactivation of extracellular signal-regulated kinase (Erk)1/2 induced by these factors affected in the process of osteosarcoma differentiation. In addition, Fgf2 enhanced both proliferation and migratory activity of osteosarcoma cells and modulated the sensitivity of cells to an anticancer drug. The results of the present study suggest that the histology of osteosarcoma tumors which consist of immature tumor cells and pathologic bone formations could be generated dependent on the distribution of such environmental factors. The combined blockade of the signaling pathways of several growth factors, including Fgf2, might be useful in controlling the aggressiveness of osteosarcoma.

Establishment of a choriocarcinoma model from immortalized normal extravillous trophoblast cells transduced with HRASV12

Gestational choriocarcinoma is a malignant trophoblastic tumor. The development of novel molecular-targeted therapies is needed to reduce the toxicity of current multiagent chemotherapy and to treat successfully the chemoresistant cases. The molecular mechanisms underlying choriocarcinoma tumorigenesis remain uncharacterized, however, and appropriate choriocarcinoma animal models have not yet been developed. In this study, we established a choriocarcinoma model by inoculating mice with induced-choriocarcinoma cell-1 (iC³-1) cells, generated from HTR8/SVneo human trophoblastic cells retrovirally transduced with activated H-RAS (HRASV12). The iC³-1 cells exhibited constitutive activation of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways and developed into lethal tumors in all inoculated mice. Histopathological analysis revealed that the tumors consisted of two distinct types of cells, reminiscent of syncytiotrophoblasts and cytotrophoblasts, as seen in the human choriocarcinoma. The tumors expressed HLA-G and cytokeratin (trophoblast markers) and hCG (a choriocarcinoma marker). Comparative analysis of gene expression profiles between iC³-1 cells and parental HTR8/SVneo cells revealed that iC³-1 cells expressed matrix metalloproteinases, epithelial-mesenchymal transition-related genes, and SOX3 at higher levels than parental trophoblastic cells. Administration of SOX3-specific short-hairpin RNA decreased SOX3 expression and attenuated the tumorigenic activity of iC³-1 cells, suggesting that SOX3 overexpression might be critically involved in the pathogenesis of choriocarcinoma. Our murine model represents a potent new tool for studying the pathogenesis and treatment of choriocarcinoma.

Abstract 409: Analysis of invasion patterns in an induced cancer stem cell model of malignant brain tumor

Background: The invasive phenotype of malignant brain tumors is a major cause for their recurrence and resistance to therapy. It has been suggested that tumor cells recapitulate the migration patterns of glial progenitors. However, it is still unclear which cells acquire a migratory potential, at which stage they acquire it and whether and how invasion patterns change during tumorigenesis and treatment. The present study aims to define the characteristics of infiltrating cells and the patterns of invasion of genetically-induced brain tumor-initiating cells (BTICs) in the syngeneic mouse adult brain.

Methods: We have established a mouse malignant brain tumor model by overexpressing RASV12 in neural stem cells/multipotent progenitor stem cells derived from the subventricular zone of mice with a homozygous deletion of the Ink4a/ARF locus. Orthotopic implantation of these BTICs into 6-week-old wild type mice resulted in formation of highly invasive, hypervascular, serially transplantable glioblastoma-like tumors with a 100% penetrance and a 5-week median survival. Fifteen mice were sacrificed at one-week intervals (n=3) and fixed brain sections were analyzed for onset and direction of cell migration. A second series of 10 mice were sacrificed at two-day intervals (n=2), and the live brains were sliced, cultured and motility and infiltration patterns were analyzed by timelapse microscopy, cell tracking and 3D reconstruction.

Results: Pathological analysis revealed that cellular migration was detectable at one week post-injection, with both movement along fiber tracts, as well as perivascular trajectories. During the later stages of tumorigenesis, invasive foci were located mostly around blood vessels and the invasive front coincided with VEGFR and HO-1 expression.

Timelapse microscopy confirmed motility of tumor cells as early as two days post- injection. Movement along blood vessels was quick and directed away from the tumor, while intraparenchymal movement was more saltatory, with repeated extension and retraction of leading processes, pausing and turning. Cells which exited the tumor early sometimes tested several routes before taking one and then exhibited a to-and-fro movement, creating paths for other cells. Motility was not affected by cell number and cells from secondary and tertiary tumors retained the infiltrative characteristics. Furthermore, co-injection of dsRed-labeled nestin-positive and GFP-labeled GFAP-positive tumor cells showed that differentiation status seems to affect infiltration patterns more than motility in itself.

Conclusion: Our results show that invasion is one of the earliest events in tumorigenesis. Moreover, the once established infiltration paths might facilitate further invasion at later stages. We therefore suggest that, to efficiently prevent recurrence, migration should be considered as a therapeutic target from the time of diagnosis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 409.

Arsenic trioxide augments Chk2/p53-mediated apoptosis by inhibiting oncogenic Wip1 phosphatase

The oncogenic Wip1 phosphatase (PPM1D) is induced upon DNA damage in a p53-dependent manner and is required for inactivation or suppression of DNA damage-induced cell cycle checkpoint arrest and of apoptosis by dephosphorylating and inactivating phosphorylated Chk2, Chk1, and ATM kinases. It has been reported that arsenic trioxide (ATO), a potent cancer chemotherapeutic agent, in particular for acute promyelocytic leukemia, activates the Chk2/p53 pathway, leading to apoptosis. ATO is also known to activate the p38 MAPK/p53 pathway. Here we show that phosphatase activities of purified Wip1 toward phosphorylated Chk2 and p38 in vitro are inhibited by ATO in a dose-dependent manner. Furthermore, DNA damage-induced phosphorylation of Chk2 and p38 in cultured cells is suppressed by ectopic expression of Wip1, and this Wip1-mediated suppression can be restored by the presence of ATO. We also show that treatment of acute promyelocytic leukemia cells with ATO resulted in induction of phosphorylation and activation of Chk2 and p38 MAPK, which are required for ATO-induced apoptosis. Importantly, this ATO-induced activation of Chk2/p53 and p38 MAPK/p53 apoptotic pathways can be enhanced by siRNA-mediated suppression of Wip1 expression, further indicating that ATO inhibits Wip1 phosphatase in vivo. These results exemplify that Wip1 is a direct molecular target of ATO.

Chk2 kinase is required for methylglyoxal-induced G2/M cell-cycle checkpoint arrest: implication of cell-cycle checkpoint regulation in diabetic oxidative stress signaling

Methylglyoxal (MG) is a reactive endogenous metabolite that is produced from the process of degradation of triose-phosphates. Under hyperglycemic conditions the rate of MG formation increases as a result of elevated concentrations of precursors. It has been established that MG elicits oxidative stress signaling, leading to the activation of MAP kinases, p38 MAPK and JNK, yet it remains largely unknown about a role of cell-cycle checkpoint regulation in MG-induced signaling. Here, we show that checkpoint kinases, Chk1 and Chk2, as well as their upstream ATM kinase are phosphorylated and activated following MG treatment of cultured cells. This MG-induced activation of Chk1 and Chk2 were inhibited by either aminoguanidine (AG), an inhibitor of production of advanced glycation end products (AGEs) or N-acetyl-l-cysteine (NAC), an anti-oxidant in dose dependent manners, indicating that oxidative stress via AGEs is involved critically in the activation of Chk1 and Chk2 by MG. Furthermore, it was found that cell-cycle synchronized cells exhibited G(2)/M checkpoint arrest following MG treatment, and that siRNA-mediated knock-down of Chk2, but not Chk1, results in a failure of MG-induced G(2)/M arrest. Thus, the results indicate a critical role for Chk2 in MG-induced G(2)/M cell-cycle checkpoint arrest.